With the increase in the development and use of mobile devices, the importance of secondary batteries as a main power source is recently growing. Among the secondary batteries, particularly lithium secondary batteries have been commercially available and widely used due to their high energy density and high voltage.
Many companies have produced a variety of electrochemical devices with different safety characteristics. It is very important to evaluate and ensure the safety of the batteries. The most important consideration for safety is that operational failure or malfunction of batteries should not cause injury to users. For this purpose, regulatory guidelines strictly restrict potential dangers (such as fire and smoke emission) of electrochemical devices. Moreover, the most urgent problem to be solved is overcharging.
All batteries are dangerous when being overcharged and lithium ion secondary batteries have no exception. Particularly, the ‘high-temperature overcharging’ of the batteries is the most dangerous. Generally, when the lithium ion secondary batteries are overcharged to 4.2V or higher, decomposition of an electrolyte solution starts and there is a high possibility of ignition when the lithium ion secondary battery reaches a high temperature of flash point.
In order to overcome this problem, various attempts have been proposed, but there is a still need for more effective solutions.